Biochem/physiol Actions Biperiden hydrochloride is antiparkinsonian; non-selective muscarinic receptor antagonist. It is used for the adjunctive treatment of all forms of Parkinson′s Disease (postencephalitic, idiopathic, and arteriosclerotic); also commonly used to improve parkinsonian signs and symptoms related to antipsychotic drug therapy. LD50 in rats 750 mg/kg; in dogs 340 mg/kg.